RuvC is the only known endonuclease to resolve the four-way DNA complex better known as the Holliday junction. X-ray crystallographic studies reveal the active site of RuvC is topologically similar to the catalytic domain of other polynucleotidyl transferases such as HIV-1 Integrase, RNAse H and MuA. We report the successful crystallization of four sequence specific RuvC-Holliday junction complexes and their Bromine and Iodine derivatives. These crystal complexes diffract to 2.8 w resolution with conventional sources. Synchrotron radiation will greatly facilitate the determination of these structures in two ways: high resolution reflections will show greater intensity over sigma values, and the highly collimated beam will decrease the amount of diffuse scattering.